Low size and weight, high power fiber laser pump

ABSTRACT

A device for cooling a laser diode pump comprising a Low Size Weight Power Efficient (SWAP) Laser Diode (LSLD) assembly, including a laser diode coupled to a submount on a first surface, the submount comprising a first thermally conductive material and a heatsink coupled to a second surface of the submount, wherein the heatsink comprises a second thermally conductive material, the heatsink comprising one or more members formed on a side opposite the coupled submount. The device further comprising a housing coupled to the LSLD assembly, the housing comprising a carrier structure having an aperture configured to support the LSLD assembly on a first side and having a plurality of channels on a second side, a bottom segment configured to couple to the carrier segment to create an enclosure around the channels between a top side of the bottom segment and the second side of the carrier structure, an inlet and outlet formed in the housing for transporting a coolant into and out of the channels in the enclosure, wherein the members are disposed within the enclosure so as to expose the members to the coolant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority from U.S.patent application Ser. No. 15/498,422, filed Apr. 26, 2017, now issuedas U.S. patent Ser. No. 10/109,978, which is a non-provisional of andclaims priority from US provisional patent application U.S. Ser. No.62/327,971 filed on Apr. 26, 2016 and US provisional patent applicationU.S. Ser. No. 62/458,569 filed on Feb. 13, 2017.

TECHNICAL FIELD

This invention relates generally to thermal management of laser diodepumps.

BACKGROUND

Most fiber-coupled laser diode pumps have been developed for largevolume industrial applications where the primary metric isprice-per-bright-watts and reliability. In conventional high-power fiberlaser technology a significant portion of the weight and volume of thetotal fiber laser system is in the high powered diode pumps where muchof that weight and volume is devoted to waste heat removal. For example,high-powered laser diode pumps are commonly cooled with chilling platesmade of highly thermally conductive material such as copper (Cu). Thisadds significant excess mass and volume to a laser system.

However, in mobile laser applications the key metrics also includevolume, weight, and electrical to optical power conversion efficiency(PCE). Moreover, industrial diode lasers are approximately 1 kg/kW andvolumes are greater than two times what would be acceptable for HighEnergy Laser (HEL) applications. Furthermore, industrial diode lasersare at approximately 50% electrical-to-optical PCE hereas, HELapplications require PCE 55%. What is needed is laser diode pumps thatare optimized for size, weight and power efficiency in addition toprice-per-bright-watts and reliability.

SUMMARY

Disclosed herein is a Low Size Weight and Power (SWAP) efficient LaserDiode pump design encompassing a shift from a dense but highthermal-conductivity solid material (e.g., copper) to lighter materialswhile keeping the opto-mechanical design and topology of a conventionalindustrial laser diode pump package to improve manufacturing outcomesand reduce manufacturing costs. Additionally, disclosed are methods ofpacking multiple laser diode pump packages together in a compact mannerto demonstrate power-scaling capability while maintaining low SWAP andhigh efficiency of the disclosed laser diode pump. Although, in theexamples provided herein a particular pump architecture is used todemonstrate the Low SWAP Laser Diode (LSLD) pump design, the conceptdescribed may be applied to a variety of pump architectures and claimedsubject matter is not limited in this regard. In an example, thedisclosed LSLD pump design uses, at least, three-times lower densitymaterials for housing, lid and thermally non-critical parts. The housingmaterial is also stiff enough that with the addition of new structuralfeatures a rigid support mechanism is in place to maintain opticalalignment while keeping mass at a minimum. Instead of using a solid basefor the package which then gets thermally coupled to yet anotherchilling plate the disclosed LSLD pump incorporates high surface-areafins (or similar structures) attached to the laser diode submount andlocated inside a hollowed-out housing to improve the thermal conductanceby three times while reducing total mass to achieve 0.5 kg/kW specificmass.

Multiple LSLD pumps may be coupled together for higher energyapplications. A manifold shared by two or more LSLD pumps may be used tointroduce coolant to remove excess heat dissipated by the fins of thetwo or more LSLD pumps. The manifold may be made of very lightweightmaterials such as Polyetheretherketone (PEEK) for example, his removesthe need for chilling plates which typically adds excess mass and volumeto laser systems. The disclosed LSLD Pump may have a 4× smallerfootprint, 10× smaller mass and 10% higher efficiency than comparableproducts available on the market.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, wherein like reference numerals representlike elements, are incorporated in and constitute a part of thisspecification and, together with the description, explain the advantagesand principles of the presently disclosed technology. In the drawings,

FIG. 1 illustrates an example of a low SWAP laser diode (LSLD) assembly;

FIG. 2A illustrates an example of a LSLD pump 200;

FIG. 2B is a partial section view of an example carrier structure of anLSLD pump magnified to show an example of optical components that may bedesigned into an LSLD pump;

FIG. 3A is a plan view of a front side of an example carrier structureof an LSLD housing;

FIG. 3B is a plan view of a backside of an example carrier structure ofan LSLD housing;

FIG. 3C is a plan view of a backside of an example carrier structure ofan LSLD housing;

FIG. 4A is a perspective view of a top side of an example of a bottomsegment of an LSLD housing;

FIG. 4B is a perspective view of an example of a backside of a bottomsegment fitted to carrier structure of housing 202;

FIG. 5A is a cross-sectional side view of an example LSLD pump;

FIG. 5B is an exploded cross-sectional side view of an example LSLD pump200;

FIG. 6 is an exploded cross-sectional side view of an LSLD pump;

FIG. 7 is a perspective view of an example of an LSLD pump having a lid;

FIG. 8 illustrates an example of a specialized heatsink for an LSLDpump;

FIG. 9A illustrates an example of a specialized heatsink for an LSLDpump;

FIG. 9B illustrates an example of a specialized heatsink material for anLSLD pump;

FIG. 9C illustrates an example of specialized heatsink members for anLSLD pump

FIG. 9D illustrates an example of a specialized heatsink for an LSLDpump;

FIG. 10A is a perspective view of an example of a plurality of LSLDpumps coupled to a manifold configured to enable the LSLD pumps to bearranged in a compact layout;

FIG. 10B is an exploded view of an example of a plurality of LSLD pumpscoupled to a manifold configured to enable the LSLD pumps to be arrangedin a compact layout;

FIG. 10C is a perspective view of an example of a plurality of LSLDpumps layered with intervening manifold and shared coolant source toenable the LSLD pumps to be arranged in a compact layout.

DETAILED DESCRIPTION

As used herein throughout this disclosure and in the claims, thesingular forms “a,” “an,” and “the” include the plural forms unless thecontext clearly dictates otherwise. Additionally, the term “includes”means “comprises.” Further, the term “coupled” does not exclude thepresence of intermediate elements between the coupled items. Also, theterms “modify” and “adjust” are used interchangeably to mean “alter.”

The systems, apparatus, and methods described herein should not beconstrued as limiting in any way. Instead, the present disclosure isdirected toward all novel and non-obvious features and aspects of thevarious disclosed embodiments, alone and in various combinations andsub-combinations with one another. The disclosed systems, methods, andapparatus are not limited to any specific aspect or feature orcombinations thereof, nor do the disclosed systems, methods, andapparatus require that any one or more specific advantages be present orproblems be solved. Any theories of operation are to facilitateexplanation, but the disclosed systems, methods, and apparatus are notlimited to such theories of operation.

Although the operations of some of the disclosed methods are describedin a particular, sequential order for convenient presentation, it shouldbe understood that this manner of description encompasses rearrangement,unless a particular ordering is required by specific language set forthbelow. For example, operations described sequentially may in some casesbe rearranged or performed concurrently. Moreover, for the sake ofsimplicity, the attached figures may not show the various ways in whichthe disclosed systems, methods, and apparatus can be used in conjunctionwith other systems, methods, and apparatus. Additionally, thedescription sometimes uses terms like “produce” and “provide” todescribe the disclosed methods. These terms are high-level abstractionsof the actual operations that are performed. The actual operations thatcorrespond to these terms will vary depending on the particularimplementation and are readily discernible by one of ordinary skill inthe art.

In some examples, values, procedures, or apparatus are referred to as“lowest”, “best”, “minimum,” or the like. It will be appreciated thatsuch descriptions are intended to indicate that a selection among manyused functional alternatives can be made, and such selections need notbe better, smaller, or otherwise preferable to other selections.Examples are described with reference to directions indicated as“above,” “below,” “upper,” “lower,” and the like. These terms are usedfor convenient description, but do not imply any particular spatialorientation.

Throughout the following disclosure lists giving examples of variouselements, materials, structures, features, or the like or anycombination thereof are provided. While these lists are representativeof the types of elements, materials, structures, features, or the likeor any combination thereof various examples may comprise, the lists areby no means exhaustive and are merely intended to elucidate thedisclosed technology and claimed subject matter is not limited in thisregard.

FIG. 1 illustrates an example of a low SWAP laser diode (LSLD) assembly100. LSLD assembly 100 comprises a laser diode 101 configured togenerate a laser beam. Laser diode 101 is coupled to submount 102 in a“Chip on Submount” (COS) formation. Submount 102 may be made of avariety of materials such as silicon carbide (SiC), chemical vapordeposition (CVD) diamond, copper (Cu), aluminum nitride (AlN), cubicboron nitride (c-BN), graphite, graphene, graphene-composites, carbonnanotubes, carbon nanotube composites, diamond or encapsulated pyrolyticgraphite, or the like or any combinations thereof. It can be shown thatthere is improvement in power and efficiency of laser diode 101 mountedon a SiC submount vs an AlN submount. Furthermore, a comparison of thejunction temperature of laser diode 101 on a SiC submount vs CVD-diamondsubmount shows CVD-diamond submount performs 25% better in thermalresistance.

In an example, submount 102 is coupled to a heatsink 104 configured totransfer heat generated by a laser diode 101 to heatsink 104. Heatsink104 may comprise any of a variety of materials such as aluminum siliconcarbide (AlSiC), pyrolytic graphite, copper (Cu), aluminum (Al), or thelike or any combinations thereof. Heatsink 104 may be fabricated out ofsomething completely different from conventional materials noted above.

Example heatsink 104 includes a plurality of members 108. As depicted inFIG. 1, members 108 comprise fins 110. In other examples, members 108can comprise any of a variety of structures having a highsurface-to-volume ratio configured for efficient heat transfer. Suchstructures include fins, posts, pegs, structures having texturedsurfaces (e.g., dimpled surfaces), or porous structures (e.g., graphitefoam or micro-porous copper (Cu)), structures constructed using additivemanufacturing to optimize surface-to-volume ratio with functionaloptimization, or the like or any combinations thereof. It is possible toreduce a conventional copper heatsink mass by about 30%, for example,from a current 1.94 g to 1.40 g per heatsink. This may amount to 30%reduction in heatsink mass and 0.27 g/W specific mass for the totalpackage. Additionally the thermal transfer coefficient may reduce to, atleast, double resulting in about 1% improvement in efficiency.

In an example, heatsink 104 may be fabricated by a variety of techniquesknown to those of skill in the art. One such technique might be computernumerical control (CNC) machining, for example. In another example,heatsink 104 may be fabricated by skiving or micro-skiving which allowsintroducing a large surface area to increase a thermal transfercoefficient. In an example, wherein the members 108 comprise fins arange of thicknesses, gaps and fin heights to optimize the thermaltransfer coefficient may be selected depending on the desired outputpower level and operating efficiency.

FIG. 2A illustrates an example of a low SWAP laser diode (LSLD) pump200. Diode pump 200 comprises a housing 202 having a carrier segment 204configured to support one or more LSLD assemblies 100. Housing 202 maycomprise a variety of rigid and lightweight materials for examplealuminum (Al), aluminum silicon carbide (AlSiC), magnesium alloys,different forms of carbon, beryllium alloys (e.g., BeO and/or BeAl), orthe like or combination thereof. Carrier structure 204 may secure theone or more LSLD assemblies 100 in apertures 212 which are formed tomate to and support corresponding LSLD assemblies 100. In an example,laser diodes 101 reside above surface 234 of carrier structure 204.

Apertures 212 are configured to securely hold one or more members 108 ofone or more LSLD assemblies 100 in channels (see FIG. 3B) formed in abackside of carrier structure 204. The channels are formed so thatcoolant can flow through them. LSLD assemblies 100 generate significantamounts of heat during operation. As coolant flows through the channelsand across the members 108 it can transfer significant amounts of heataway from LSLD assemblies 100. Because heat is transferred veryefficiently to members 108 in contact with coolant flowing through thechannels, LSLD pump 200 may operate more efficiently, with lower massflow and lower pressure drop than a conventional laser diode pump havingonly a solid thermally conductive heatsink that is not in contact with aflowing coolant.

In an example, each LSLD assembly 100 is attached to an inner surface ofa corresponding aperture 212 by gluing, soldering, brazing, welding orthe like or a combination thereof. Surface 234 may be a flat plate ormay comprise a vertical stair step structure as shown in FIG. 2A. Withsuch a stair step arrangement, each aperture 212 into which the LSLDassemblies 100 are disposed can be on a separate stair so that the beamsemanating from the LSLD assemblies 100 can be spatially separated fromone another. Thus, LSLD assemblies 100 may be disposed relative to oneanother in a stepwise fashion. In another example, a plurality ofcavities 212 may reside on a single stairstep in order to support aplurality of laser diodes 100 at each stairstep level.

In an example, bottom segment 206 may form a sealed chamber when coupledwith carrier structure 204. Bottom segment 206 and carrier structure 204may be coupled at lip 210 (and/or other locations) by a variety ofmethods such as welding, brazing, gluing, or friction or the like, orany combination thereof.

One or more laser diodes 101 are carefully aligned with a variety ofoptical components within housing 202. FIG. 2B illustrates a partialsection view of carrier structure 204 enlarged to show an example ofoptical components that may be designed into LSLD pump 200. Thefollowing example includes laser diodes and corresponding opticalcomponents stacked in the vertical axis on stair steps. The number oflaser beams and stair steps chosen depends on the desired output powerlevel and operating efficiency of the LSLD pump 200. The partial sectionview shown in FIG. 2B shows three laser diodes and stair steps. However,any reasonable number of laser diodes may be included in LSLD pump 200and claimed subject matter is not so limited. Such optical componentsmay comprise fast axis collimating (FAC) lenses 222 a-c, slow axiscollimating (SAC) lenses 224 a-c, angled reflective surfaces 226 a-c,turning mirrors 230 a-c, a polarization multiplexer (P-MUX) 236, ameniscus fast axis telescope (mFAT) 228, ferrule 248 and light absorbingelement 238.

In an example, each fast axis collimating (FAC) lens 222 a-c is forcollimating respective laser beams 240 a-c generated by laser diodes 101a-c in the fast axis. Slow axis collimating (SAC) lenses 224 a-c are forcollimating respective laser beams 240 a-c in the slow axis. The angledreflective surfaces 226 a-c are for directing retro-reflecting or straylight to a bottom surface 234 of carrier structure 204 so that it can beabsorbed and the resultant heat dissipated to a coolant in coolantportion 206. Turning mirrors 230 a-c are for directing respective laserbeams 240 a-c toward P-MUX 236. Turning mirrors 230 a-c maybe angled atany of a variety of angles sufficient to direct laser beams 240 a-ctoward P-MUX 236. P-MUX 236 is configured for directing laser beams 240a-c toward the input surface of fiber 232. mFAT 222 a-c are fortelescoping laser beams 240 a-c toward the input surface of fiber 232.mFAT 222 a-c reduce standard two-element Galilean telescope to a singlemeniscus lens thereby reducing the number of elements that must bealigned with respect to each other. In another example, standardtwo-element Galilean telescope lenses may be used instead of the mFAT222. Light absorbing element 238 is a nonreflective and absorbingmaterial for absorbing residual light that may leak out of P-MUX 236.Fiber ferrule 248 helps to direct laser beams 240 a-c into fiber 232.

In an example, laser diodes 222 a-c are each disposed on a differentstairstep 242, 244 and 246. With this configuration, laser beam 240 a isprojected over turning mirrors 230 b and 230 c and laser beam 240 b isprojected over turning mirror 230 c. Laser beams 240 a-c are transmittedinto PMUX 236. Thus, laser beams 240 a-c stack up in the verticaldirection in the collimated space with nearly 100% fill factor.

In an example, LSLD pump 200 may be configured with two rows of stairstepped laser beams stacked vertically with one row per polarizationusing P-MUX 236 to achieve two times the brightness. Laser beams 240 a-care then focused into a fiber using a combination of telescope andfocusing lens. Such a stairstep configuration provides a compact andefficient configuration of the laser diodes and optical elements in LSLDpump 200. Each laser beam 240 a-c is individually lensed thus enablingbeam-pointing that is not possible with bar technology. Bars haveinherent “smile” issues which result in “rogue” beams that are notunidirectional, degrade beam quality and introduce high numericalaperture cladding-light when coupled into fibers. This is significantlydifferent from the currently described optical assembly of LSLD pump 200which can achieve under-filled numerical aperture and spot size whenfocused into a fiber thus eliminating the need for cooling the deliveryfiber. This optical combining method is very efficient and it conservesvolume since no large opto-mechanical components are required to arrangethe laser beams 240 a-c into a compact and nearly 100%-fill-factorcollimated beam format—a requirement before focusing for efficient andhigh brightness operation. This stair-step arrangement provides asimple, multiple-beam compactification method which achieves low volumeand clearly distinguishes the disclosed method compared to bar-basedcoupling scheme.

In an example, one or more rigid support structures 214 are formed alongsidewalls 216 of carrier structure 204. Rigid support structures 214 areformed to provide support to the carrier structure 204 to preventdeformation during operation when heating of carrier structure 204 orother housing 202 structures may occur. Deformation due to heating ofcarrier structure 204 may cause misalignment of optical componentsdescribed above with respect to FIG. 2B, among other problems. Rigidsupport structures 214 a-c are formed within respective angled sections215 a-c to promote redirection of stray light during operation of LSLDpump 200. A portion of light reflected off of angled sections 215 a-cmay be absorbed by surfaces 214 a-c, 215 a-c and 234 and the heatgenerated by that absorption may be transferred to coolant flowingthrough the channels described in greater detail with respect to FIGS.3B and 3C.

Returning to FIG. 2A, housing 202 also may include an inlet 218 andoutlet 220 formed in carrier structure 204 of housing 202 fortransporting coolant into and out of the channels formed on the backsideof carrier structure 204. The channels may be enclosed by bottom segment206. Such enclosure may be referred to herein as a cooling manifold(shown in more detail in FIG. 5A). Members 108 are disposed within thecooling manifold enabling members 108 to be exposed to coolant withoutexposing laser diode 101 to the coolant.

FIG. 3A illustrates a plan view of a front side 310 of an examplecarrier structure 204 of housing 202. LSLD assemblies 100 are not shownso that cavities 212 can be more easily visualized. Channel walls 302disposed on the underside of carrier structure 204 can be seen throughcavities 212.

FIG. 3B illustrates a plan view of a backside 304 of an example carrierstructure 204 of housing 202. In an example, one or more channels 306are configured to guide a coolant across members 108 to transfer heataway from LSLD assembly 100. Bottom segment 206 may form a sealedchamber around channels 306 when coupled with carrier structure 204.Coolant may flow in the direction of arrows 308 from an area of higherpressure to an area of lower pressure for example from inlet 218 tooutlet 220. Cooling is reconfigurable to achieve a range of pressuredrops and commensurate mass flow rate to maintain desired heat removalcapacity and temperature difference across the coolant. Therefore theexact design of the channels 306 is versatile. For example, FIG. 3Cshows a channel design wherein channels 306 are configured three acrossin a serpentine formation from inlet 218 to outlet 220. The materialsforming the cooling channels can be coated so that many types ofcoolants can be used, for example, water, water and either ethyleneglycol (EGW) or propylene glycol (PGW), ammonia, or1,1,1,2-Tetrafluoroethane (R134A), or the like or any combinationthereof.

Example Channel Configurations

In table 1 below a number of example channel configurations for 0.9kg/min/kW are provided. In Table 2 is modeled thermal performance forthree examples of channel configurations for LSLD pump 200 using an SiCsubmount 102 and finned-copper heatsink 104, achieving similar thermalperformance at the same water flow rate but under different pressuredrop.

TABLE 1 MASS FLOW Power No. in ΔP per Pump Total ΔP ΔT per Total ΔT inRATE (W)/Pump Series (PSI) (PSI) Pump(K) Series (K) (kg/min/kW) 360 41.67 6.7 3.98 15.9 0.74 360 5 1.11 5.6 2.65 13.3 0.89 480 4 1.67 6.75.30 21.2 0.55 480 5 1.67 8.3 5.30 26.5 0.44 600 4 1.00 4.0 3.98 15.90.74 600 5 1.00 5.0 3.98 19.9 0.59

TABLE 2 Water Pres- Water Average Average Temperature sure Flow DiodeThermal Diode Cooling Rise Drop Rate Temperature ResistanceConfiguration (° C.) (PSI) (GPM) (° C.) (° C./W) 15 in parallel 7.0 0.080.21 30 1.1 2 in series 5 in parallel 7.0 0.88 0.21 29 1.1 6 in series 3in parallel 7.0 2.67 0.21 28 1.0 10 in series

FIG. 4A illustrates a perspective view of topside 410 of an examplebottom segment 206. In an example, bottom segment 206 has a staircaseshape that is similar to the staircase shape of carrier structure 204.In other examples bottom segment 206 may have different conformationsdepending on the particular design of LSLD pump 200. Bottom segment 206is configured to mate to carrier structure 204 fitting inside of carrierstructure 204 with lip 412 extending around a bottom edge of carrierstructure 204.

FIG. 4B illustrates a perspective view of an example of a backside 402of bottom segment 206 fitted to carrier structure 204 of housing 202.Backside 402 has one or more voids 400 formed by a variety of methodsknown to those of skill in the art such as machining, chemical etching,3D manufacturing, forging, die-casting or the like or combinationsthereof. The voids 400 are formed to reduce the weight of LSLD pump 200while providing structural support to housing 202 in order to preventdeformation of bottom segment 206 and/or other portions of housing 202.Such deformation may have devastating effects on critical opticalalignments, for example, of the laser diode 101 with various opticalcomponents precisely positioned within housing 202 as described abovewith respect to FIG. 2B.

The voids 400 may be of a variety of shapes and sizes. In some examples,voids 400 may be hexagonal and arranged in a honeycomb or may be squareand arranged in a grid as depicted in FIG. 4B. In other examples, theone or more voids 400 may comprise any of a variety of geometricalshapes standing alone, tiled or otherwise arranged together to optimizestiffness for lowest mass. Tiling may be done in a regular repeatingpattern or in an aperiodic pattern. In an example, the shape(s) of theone or more voids 400 may be selected to optimize structural supportand/or weight or volume reduction of housing 202. Because bottom segment206 has a staircase shape as shown in FIG. 4A, the depth of voids 400 isshallower where the stairstep height is lower and as the stairstepheight increases so too does the depth of voids 400. In another example,bottom segment 206 may be flat and the one or more voids 400 may be thesame or similar depths.

FIG. 5A is a longitudinal cross-sectional side view of LSLD pump 200. Inan example, LSLD assemblies 100 are disposed in apertures 212 of carrierstructure 204. Members 108 extend into channels 306 which are enclosedby top surface 410 of bottom segment 206. Bottom segment 206 isconfigured to mate to carrier structure 204 fitting inside of carrierstructure 204 with lip 412 extending around a bottom edge of carrierstructure 204. The assembly of carrier structure 204 and bottom segment206 may be a tight fit sufficient to create a seal and/or barrier toleakage of coolant out of channels 306. Top surface 410 may be coupledto carrier structure 204 by a variety of methods for example by a closefit, welding, brazing, soldering and the like or any combinationsthereof. Channel 306 heights are defined by the distance between surface234 of carrier structure 204 and top surface 410 of bottom segment 206.Thus, channel 306 heights are substantially uniform. Voids 400 havevarying heights/volumes depending on the height of a corresponding stairstep.

FIG. 5B is an exploded longitudinal cross-sectional side view of LSLDpump 200. In an example, carrier structure 204 wall 502 is configured tofit snugly around bottom segment 206 wall 504. Coupling of wall 502 withwall 504 may create a seal sufficient to prevent coolant leakage fromchannels 306. Again, as noted above carrier structure 204 may be coupledto bottom segment 206 by a variety of methods including friction,welding, brazing, soldering, laser welding, seam-sealing or the like, orany combination thereof. In an example, LSLD pump 200 may achieve 0.5kg/kW specific mass.

FIG. 6 is an exploded cross-sectional side view of LSLD pump 200. In anexample, LSLD assembly 100 is disposed in aperture 212. Heatsink 104rests on lip 602 of aperture 212 such that members 108 extend intochannel 306. Channels 306 are defined by channel walls 302.

FIG. 7 illustrates an example of a LSLD pump 200 having a lid 700 forenclosing the LSLD pump 200 system. Lid 700 is a thermally noncriticalpart and may comprise low-density material.

Topological Optimization of Heatsink

FIG. 8 illustrates an example of a specialized heatsink 806 for LSLDassembly 800 for implementation in LSLD pump 200. In an example,heatsink 806 may be made from a variety of thermally conductivematerials such as AlSiC, AlBe, pyrolytic graphite, annealed pyrolyticgraphite (APG), encapsulated APG, Cu, Al, Si or the like or anycombinations thereof. Members 808 may comprise pegs or posts having ahigh surface area-to-volume ratio to enable removal of excess heat froma laser diode/submount assembly (not shown) as discussed above. The pegsor posts may be any of a variety of shapes such as square, rectangular,polygonal or circular or the like or any combination thereof. Thisconfiguration may further reduce the weight of the LSLD pump 200 andincrease the thermal transfer coefficient over fin shaped members 108.In this way, the thermal performance may be further improved and weightreduced.

FIG. 9A depicts an example heatsink 806 (see FIG. 8) material forincreasing surface area to come into contact with a coolant for coolingLSLD pump 200. Graphite foam 900 is a lightweight structure with highthermal conductivity. In an example, heatsink 806 and/or members 808 maycomprise graphite foam 900. The graphite foam 900 may be coupled tosubmount 102 by brazing, soldering, laser welding, or the like or anycombination thereof.

FIG. 9B depicts an example heatsink 806 material for increasing surfacearea to come into contact with a coolant for cooling LSLD pump 200.Microporous copper 902 is lightweight with 80% porosity, has highthermal performance, and requires little processing in order to prepareit for use. Heatsink 104 and/or members 108 may comprise microporous Cu902. The microporous Cu 902 may be coupled to submount 102 by brazing,soldering, laser welding, or the like or any combinations thereof.

FIG. 9C depicts example members 808 of heatsink 806 comprising variousshapes. In an example, members 808 may comprise an elongated wedge 904,a parabolic cone 906 and/or a bottleneck 908 that may improve thermaltransfer by increasing surface-area-to-volume ratio, turbulent flowand/or promote more complete transfer of heat throughout a coolant inclose proximity with the members 108. Members 808 may take on any one ofthe shapes 904, 906, or 908 or may have a variety of shapes on a singleheatsink including 904, 906 and/or 908 in heatsink 104. However, theseare merely examples, many other shapes may be configured to optimize thevariables noted above and claimed subject matter is not limited in thisregard.

FIG. 9D depicts example members 808 formed using computer modeling and3D manufacturing techniques. Such computer modeling techniques may beable to identify a “3D topologically optimized structure” for aparticular laser power, coolant substance, and/or laser diode pumparchitecture. Modeling enables optimizing thermal transfer byidentifying structures to increase surface-area-to-volume ratio,turbulent flow and/or promote more complete transfer of heat throughouta coolant, as well as other factors promoting thermal transfer. In anexample, members 808 may be formed by micro-machining or 3Dmanufacturing silicon or other materials known to those of skill in theart. Silicon is less costly than copper and fabrication of 3D structuresin silicon is also relatively easier compared to machining copper sincesilicon can be micro-machined at a wafer-level.

Cooling Manifold

FIGS. 10A-10C depict examples of a plurality of LSLD pumps sharing oneor more cooling manifold 1000.

FIG. 10A depicts an example manifold 1000 coupled between two LSLD pumps1002. LSLD pumps 1002 are similar to LSLD pumps 200 described above,however in this example, LSLD pumps 1002 have a 2×6 arrangement of LSLDassemblies 100. In an example, manifold 1000 may comprise lightweightmaterial, for example PEEK, plastic, polypropylene, glass, fiber-glass,or the like or any combinations thereof. Manifold 1000 may be used tointroduce coolant to remove excess heat dissipated by the heatsinks 1006(see FIG. 10B) of both LSLD pumps 1002. Heatsinks 1006 are similar toheatsinks 104 described above with respect to FIG. 1. Including amanifold 1000 reduces the need for a chilling plate or other additionalheat transfer devices which typically add excess mass and volume tolaser diode pump systems. Manifold 1000 can be designed in numerousdifferent configurations depending on the available volume allocationand the shape of the volume for multi-kilowatt systems.

FIG. 10B is an exploded view of LSLD pumps 1002 and manifold 1000. Oneof the LSLD assemblies 100 and apertures 1012 are visible in upper LSLDpump 1002. Manifold 1000 has channels 1014 sized to permit alignmentwith members 1022 (e.g., fins or the like as described above) ofheatsinks 1006 for directing coolant around and through the structuralfeatures of members 1022. As described above, members 1022 may be any ofa variety of shapes, materials, and/or 3D structures as discussedhereinabove. In the current example members 1022 are fins. Inlet ports1016 and outlet port 1018 supply coolant to the channels 1014. Inanother example, and depending on the needs of application inlet ports1016 and outlet port 1018 may be reversed wherein ports 1016 may be theoutlet ports and port 1018 may be the inlet port.

Another strategy is to stack multiple LSLD pumps 1002 and manifold 1000one on top of the other. FIG. 10C is a perspective view of an example ofa plurality of LSLD pumps layered with intervening manifold 1000 andcommon manifold 1030 to enable the LSLD pumps 1002 to be arranged in acompact layout. This type of packing configuration is useful forapplications where available space is very tight. In this particularconfiguration, with a 150 W output per LSLD pump 1002, a total of 2100 Wcan be generated in a total volume of 1355 cm³ resulting in ˜1.55 W/cm³.These high brightness diodes can be combined using a commercial 7×1fiber-combiner to produce ˜1 kW output from a 220 μm and 0.22 NA beam.Then using a 6+1:1 combiner, a total of 6 kW of pump can be deployedinto a 400 μm and 0.46 NA DC fiber amplifier to produce 5 kW of singlemode output. There are yet other configurations that can be invoked tobefit a particular volume size and shape requirement.

In view of the many possible embodiments to which the principles of thedisclosed invention may be applied, it should be recognized that theillustrated embodiments are only preferred examples of the invention andshould not be taken as limiting the scope of the invention. Rather, thescope of the invention is defined by the following claims. We thereforeclaim as our invention all that comes within the scope and spirit ofthese claims.

The invention claimed is:
 1. A device comprising: a Low Size WeightPower Efficient (SWAP) Laser Diode (LSLD) assembly, including: a housingassembly, comprising: an enclosure; a carrier structure comprising aplurality of coolant channels disposed within the enclosure; and aplurality of laser diodes in contact with respective ones of a pluralityof heatsinks, wherein the heatsinks comprise cooling members that extendinto the enclosure and are disposed within respective coolant channelsof the plurality of coolant channels configured to direct a flow of acoolant within the cooling channels.
 2. The device of claim 1, whereinthe plurality of coolant channels are inline and configured to cause acoolant to flow in a single direction across the plurality of heatsinks.3. The device of claim 1, wherein the plurality of coolant channels areconfigured to follow a serpentine path and to cause a coolant to flowacross at least two different heatsink members in opposite directions.4. The device of claim 1, further comprising a bottom segment configuredto couple to the carrier structure to form the enclosure.
 5. The deviceof claim 4, wherein the bottom segment comprises at least one voidoutside of the enclosure.
 6. The device of claim 5, wherein the bottomsegment comprises a plurality of voids outside of the enclosure, whereinthe voids are rectangular and form a grid.
 7. The device of claim 6,wherein the bottom segment comprises a plurality of voids outside of theenclosure, wherein the voids are of various depths.
 8. The device ofclaim 4, wherein the carrier structure or the bottom segment arestepped, or a combination thereof.
 9. The device of claim 1, wherein thecooling members comprise a plurality of fins.
 10. The device of claim 1,wherein the cooling members comprise a microporous copper structure. 11.The device of claim 1, wherein the cooling members comprise a graphitefoam.
 12. The device of claim 1, wherein the cooling members compriseposts.
 13. The device of claim 1, wherein cooling members comprise athree-dimensional structure optimized for surface area to volume,turbulent flow and thermal transfer throughout the coolant.
 14. Thedevice of claim 1, wherein the coolant comprises water, water andethylene glycol (EGW), water and propylene glycol (PGW), ammonia, or1,1,1,2-Tetrafluoroethane (R134A) or any combination thereof.
 15. Thedevice of claim 1, wherein the plurality of heatsinks comprises aluminumsilicon carbide (AlSiC), pyrolytic graphite, annealed pyrolytic graphite(APG), encapsulated APG, copper (Cu), aluminum (Al), or any combinationthereof.
 16. The device of claim 1, wherein the plurality of heatsinksare coupled to respective submounts of a plurality of submounts,respective cooling members are formed on a side opposite the respectivecoupled submount, and the plurality of submounts comprise siliconcarbide (SiC), chemical vapor deposition (CVD) diamond, copper (Cu),aluminum nitride (AlN), cubic boron nitride (c-BN), graphite, graphene,graphene-composites, carbon nanotubes, carbon nanotube composites,diamond, diamond composites or pyrolytic graphite or any combinationthereof.
 17. The device of claim 16, wherein at least one of theplurality of submounts comprise a first thermally conductive material,at least one of the plurality of heatsinks comprise a second thermallyconductive material and the first thermally conductive material and thesecond thermally conductive material are different.
 18. A laser pumpassembly, comprising: a plurality of LSLD pumps each comprising aplurality of laser diodes in contact with respective ones of a pluralityof heatsinks, wherein each heatsink comprises cooling members extendinginto a respective coolant channel of a plurality of coolant channelsdisposed in a common manifold wherein at least two LSLD pumps share thecommon manifold.